Quantum Effect Device Research Team

Principal Investigator

PI Name Koji Ishibashi
Degree D.Eng.
Title Team Leader
Brief Resume
1988 D.Eng., Graduate School of Electrical Engineering, Osaka University
1988 Researcher, Frontier Research Program, RIKEN
1991 Researcher, Semiconductor Laboratory, RIKEN
1996 Visiting Researcher, Delft University of Technology, The Netherlands (until 1997)
2003 Chief Scientist, Advanced Device Laboratory, RIKEN (-present)
2003 Adjunct Professor, Chiba University (-present)
2005 Adjunct Professor, Tokyo University of Science (-present)
2013 Team Leader, Quantum Effect Device Research Team, Quantum Information Electronics Division, RIKEN Center for Emergent Matter Science (-present)


We study quantum effects that appear in nanoscale structures and apply them to functional nanodevise. We focus on hybrid nanostructures, such as carbon nanotube/molecule heterostructures and topological insulator or nanostructures/superconductor hybrid nanostructures as well as nanoscale Si transistors, to study quantum effects and to realize unique functionalities that enable us to control electrons, photons, excitons, and Cooper pairs on a single quantum level. With those, we develop quantum information devices and study physics behind them for future low-power nanoelectronics.

Research Fields

Engineering, Physics


Carbon nanotube
Semiconductor nanowire
Quantum dots
Topological superconductor
Quantum information devices


Towards Majorana qubit with superconductor/InAs nanowire hybrid structures

 To maintain quantum coherence is an essential requirement for the quantum computer. But, it is really a tough requirement because of decoherence and noise that could easily induce error in the computing processes. Majorana zeromodes (MZMs), simply mentioned as Majorana fermion, could help to solve this difficulty as it is predicted to be robust against such local disturbance. Although Majorana fermion has not convincingly been demonstrated, we are trying to search for it in the superconductor/semiconductor nanowire and/or superconductor/topological insulator hybrid structures, in order to realize the “Majorana qubit”. The figure shows a SNS (Super-Normal-Super) type Josephson junction with a InAs nanowire grown by molecular beam epitaxy (MBE) technique followed by the in-situ deposition of the Al contacts. We are trying to measure the energy spectrum of the MZMs by fabricating the RF-SQUID with the nanowire JJ and coupling it to the microwave resonator. This work has been carried out in collaboration with Prof. Thomas Schäpers in Julich Research Center in Germany.


Scanning electron microscope image of the InAs nanowire Josephson junction with Al contacts


Towards hybrid quantum information devices with quantum dots in a microwave resonator

We study quantum dots interacting with microwave photons in a superconducting coplanar waveguide resonator for the future hybrid quantum information devices. The quantum dot, or an artificial atom in other words, can realize a large electron-photon interaction at a single quanta level simply because the size of the artificial atom is much larger than natural atoms. Then, entanglement between an electron and a photon would be possible, a key requirement for quantum information processing. The single spin-photon interaction is also being explored with a help of a spin-orbit interaction (SOI). We use InSb or Ge/Si nanowire quantum dots that have a large SOI and are placed in a resonator (see fig). The double dot is formed by applying gate voltages on the finger gates underneath the nanowire. We measure microwave transmission at low temperatures (~100mK), and study resonant characteristics that are affected by microscopic charge (or spin) states of the double quantum dot. At this moment, we observe an charge-photon interaction with less than single photon in a resonator, but have not succeeded in realizing coherent interaction because of a large decoherence in the quantum dot.


Scanning electron microscope image of the Ge/Si nanowire quantum dots embedded in a superconducting coplanar waveguide resonator.


Koji Ishibashi

Team Leader kishiba[at]riken.jp

Keiji Ono

Senior Research Scientist

Russell Stewart Deacon

Senior Research Scientist

Patrick Ferdinand Zellekens

Special Postdoctoral Researcher


  1. M. D. Randle, M. Hosoda, R. S. Deacon, M. Ohtomo, P. Zellekens, K. Watanabe, T. Taniguchi, S. Okazaki, T. Sasagawa, K. Kawaguchi, S. Sato, and K. Ishibashi

    Gate-Defined Josephson Weak-Links in Monolayer WTe2

    Adv. Mater. 35, 2301683 (2023)
  2. P. Zellekens, R. Deacon, P. Perla, D. Gruetzmacher, M. I. Lepsa, T. Schaepers, and K. Ishibashi

    Microwave spectroscopy of Andreev states in InAs nanowire-based hybrid junctions using a flip-chip layout

    Commun. Phys. 5, 267 (2022)
  3. A. Hida, and K. Ishibashi

    Exciton Controlled-NOT Gate Using Coupled Quantum Dots in Carbon Nanotube

    ACS Photonics 9, 3398–3403 (2022)
  4. R. Wang, R. S. Deacon, J. Sun, J. Yao, C. M. Lieber, and K. Ishibashi

    Gate Tunable Hole Charge Qubit Formed in a Ge/Si Nanowire Double Quantum Dot Coupled to Microwave Photons

    Nano Lett. 19, 1052 (2019)
  5. R. S. Deacon, J. Wiedenmann, E. Bocquillon, F. Dominguez, T. M. Klapwijk, P. Leubner, C. Bruene, E. M. Hankiewicz, S. Tarucha, K. Ishibashi, H. Buhmann, and L. W. Molenkamp

    Josephson Radiation from Gapless Andreev Bound States in HgTe-Based Topological Junctions

    Phys. Rev. X 7, 021011 (2017)



2-1 Hirosawa, Wako, Saitama 351-0198 Japan